28 bulletin: museum of comparative zoology. 



queut degradation of the limestone, 1 and the actual upward movements 

 outnumber those which can be observed. 



Of all the elevations the trace of the last upheaval is specially well 

 preserved in several of the islands. Speaking very generally, it occurs 

 approximately at the same height above high-water mark in the group. 



At Ovalau an old reef is exposed in a small creek at the back of the 

 main hotel. This watercourse has cut through a loosely aggregated 

 mass of andesite blocks and pebbles, several feet in thickness, and now 

 runs along a coral floor exposed by its own erosive and denuding action. 

 This raised coral floor is almost indistinguishable from the modern reef- 

 flat. The highest tides do not quite cover it. 



At Vatu Leile the evidence of a recent uplift is undeniable. It can 

 be seen on the eastern edge of the island in the form of a flat removed 

 but a few feet from the reach of the tides (Plate 29). On the west it 

 takes the form of an enormous groove extending for miles, flat underfoot 

 and arched overhead (Plates 28, 31). At Yathata we have the same evi- 

 dence as at Vatu Leile, and at Lakemba we have an extensive flat stretch- 

 ing along the south of the island and reaching from the present reef inland 

 as far as the foot of the volcanic slopes (Plate 34). 



If we consider the vertical cliffs of Lau as the original steep submarine 

 slopes rather than due to sub-aerial and beach erosion subsequent to their 

 upheaval, then it seems reasonable to accept a much smaller loss to the 

 islands by erosion than a first glance would appear to justify. Some of 

 the islands are known to consist of limestone masses topped by sub- 

 horizontal caps. The terraces, again, of the older cliffs appear from 

 certain points as perfect level plains (Thithia, Tuvutha, Yathata), and 

 the truncated cone structures of some island masses suggests the contour 

 of the original reef. 



If we admit the persistence in the general level of such raised plat- 

 forms as Tuvutha, Vatu Vara, and Yathata, and of the original slope of 

 the raised reefs, then the amount of loss by erosion seems confined to 

 such pits and cracks as are seen on the summit of Vatu Vara, which 



1 A. Agassiz, I. c, pp. 58, 78. 



